/*
 * Copyright 2002-2014 the original author or authors.
 *
 * Licensed under the Apache License, Version 2.0 (the "License");
 * you may not use this file except in compliance with the License.
 * You may obtain a copy of the License at
 *
 *      http://www.apache.org/licenses/LICENSE-2.0
 *
 * Unless required by applicable law or agreed to in writing, software
 * distributed under the License is distributed on an "AS IS" BASIS,
 * WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
 * See the License for the specific language governing permissions and
 * limitations under the License.
 */

package qunar.tc.bistoury.instrument.client.spring.el;


/**
 * Represents a node in the Ast for a parsed expression.
 *
 * @author Andy Clement
 * @since 3.0
 */
interface SpelNode {

    /**
     * Evaluate the expression node in the context of the supplied expression state
     * and return the value.
     *
     * @param expressionState the current expression state (includes the context)
     * @return the value of this node evaluated against the specified state
     */
    Object getValue(ExpressionState expressionState) throws EvaluationException;

    /**
     * Evaluate the expression node in the context of the supplied expression state
     * and return the typed value.
     *
     * @param expressionState the current expression state (includes the context)
     * @return the type value of this node evaluated against the specified state
     */
    TypedValue getTypedValue(ExpressionState expressionState) throws EvaluationException;

    /**
     * Determine if this expression node will support a setValue() call.
     *
     * @param expressionState the current expression state (includes the context)
     * @return true if the expression node will allow setValue()
     * @throws EvaluationException if something went wrong trying to determine
     *                             if the node supports writing
     */
    boolean isWritable(ExpressionState expressionState) throws EvaluationException;

    /**
     * Evaluate the expression to a node and then set the new value on that node.
     * For example, if the expression evaluates to a property reference, then the
     * property will be set to the new value.
     *
     * @param expressionState the current expression state (includes the context)
     * @param newValue        the new value
     * @throws EvaluationException if any problem occurs evaluating the expression or
     *                             setting the new value
     */
    void setValue(ExpressionState expressionState, Object newValue) throws EvaluationException;

    /**
     * @return the string form of this AST node
     */
    String toStringAST();

    /**
     * @return the number of children under this node
     */
    int getChildCount();

    /**
     * Helper method that returns a SpelNode rather than an Antlr Tree node.
     *
     * @return the child node cast to a SpelNode
     */
    SpelNode getChild(int index);

    /**
     * Determine the class of the object passed in, unless it is already a class object.
     *
     * @param obj the object that the caller wants the class of
     * @return the class of the object if it is not already a class object,
     * or {@code null} if the object is {@code null}
     */
    Class<?> getObjectClass(Object obj);

    /**
     * @return the start position of this Ast node in the expression string
     */
    int getStartPosition();

    /**
     * @return the end position of this Ast node in the expression string
     */
    int getEndPosition();

}
